1. Field of the Invention
The present invention relates to rolling pins for abrading machines. More specifically, the sure-seal rolling pin assembly is primarily intended for use with lapping, polishing, and grinding machines to protect the ball bearings from abrasive contamination during lapping and polishing operations and to maximize the size of the pins used in such operations.
2. Description of the Prior Art
In the art of abrading machines, double-sided planetary lapping and polishing machines use involute gearing mechanisms to drive work carriers nested between a sun gear and a ring gear. Work pieces that are being processed on the machines are dragged by the work carriers in a serpentine path between an upper lap plate and a lower lap plate charged with abrasives. Although involute gearing provides near perfect meshing in an ideal environment, it has its problems in planetary lapping and polishing machines.
Gear teeth on both the sun gear and the ring gear wear out quickly and unevenly due to the continuous meshing between the work carriers and the sun gear and ring gear. The presence of the abrasives used during lapping and polishing operation deteriorates the excess wear. Besides, involute gears, especially ring gears with internal teeth, are very expensive to manufacture. If a tooth is worn out, the whole gear must be replaced. For this reason, pin gears have become popular.
A pin gear has a gear body and a plurality of vertically projecting pins mounted on the gear body. Each pin functions as a gear tooth and meshes and drives sprocket-type work carriers. Many prior double-sided lapping and polishing machines utilized this type of pin gear drive to provide motion to the work carriers. This conventional pin drive has an advantage over involute gears in that pins can be separately replaced when worn out. U.S. Pat. Nos. 4,315,383 and 4,974,370 are examples of double-sided lapping and polishing machines using pin drives.
Conventionally, there are three types of pins used in pin gears, i.e. fixed pins, sliding pins, and rolling pins. Fixed pins have been widely used due to their low cost to manufacture. However, fixed pins have a decided disadvantage that the pins and their mating components or work carriers, are worn out very quickly due to their severe sliding actions. The friction of this severe sliding action not only deteriorates the pins themselves, but also wears the teeth of the work carriers and generates particle contamination harmful to lapping, polishing and grinding processes. The particles scratch surfaces of work pieces and deteriorate their finish.
To reduce the wear between the pins and the work carriers, sliding pins have also been used on some planetary lapping and polishing machines. The sliding pins employ a bushing type of sleeves similar to those in roller chains. Theoretically, if sleeves and pins are properly lubricated, then the sliding occurs between the sleeves and the pins instead of between the sleeves and the teeth of work carriers, hence the wear on the teeth of the work carriers and the sleeves can be minimized. However, in abrading machines of the type employing pin drives, the friction between the sleeves and the pins are often higher than the friction between the sleeves and the work carriers due to the poor lubrication caused by the presence of abrasive during normal operation.
Rolling pins are therefore used to overcome the problems associated with fixed and sliding pins. The rolling pins use miniature ball bearings between sleeves, or rings, and the pins themselves. The ball bearing provides a rolling element which virtually eliminates the friction between the sleeve or ring and the pin, and therefore, the ball bearing eliminates sliding action between the sleeves or rings and the work carriers. Rolling pin gears can therefore, significantly prolong the life expectancy of not only the pins themselves but also the work carriers. An additional benefit is the reduction of particle contamination when a rolling pin is used compared to other planetary gear drives.
U.S. Pat. No. 4,974,370 is an example of a double-sided lapping and polishing machine having drive pins 26 and 28. Drive pins 26 and 28 consist of a headed bolt 29, the reduced shank portion 30 of which is adapted to be threaded into a tapped aperture formed in an inner gear 25 and an outer gear ring 27 respectively. A ball bearing supported drive ring 31 is journalled on the bolt 29 between the bolt's enlarged head and a retaining washer 32. This construction, however, does not provide a sealing feature to prevent the bearings from abrasive contamination during normal lapping and polishing operation. Conventional seals, like O-rings, do not work in rolling pins because slurries of fine abrasives and the like will penetrate into the clearances between the seals and the pins, and will eventually bond the seals and pins together.
Furthermore, small pitch in the pin gears of a lapping and polishing machine is desired in order to have smooth gearing between the ring and sun gears and the work carriers and therefore to minimize the speed fluctuation of the work carriers. Small pitch of pin gears is the distance between adjacent pins as measured from substantially similar points on each pin. In order to achieve a small pitch of pin gears in the '370 drive pins 26 and 28, the diameter of the headed bolts must be small enough so that miniature ball bearings, can fit around the outer surface of each bolt and fit within the space between adjacent pins. However, this smaller diameter reduces the rigidity of each pin and its ability to drive the work carriers due to meshing forces on the pins. In addition, the apertures, where the '370 drive pins 26 and 28 are placed on the inner gear 25 and the outer gear ring 27 respectively, must be tapped and therefore are expensive to manufacture.
Lastly, in order that the work carriers mesh, or ride and rotate, properly about the drive pins and due to wear of the upper and lower plates of the lapping and polishing machine, the elevation of the work carriers, meaning the vertical adjustment, must be adjusted from time-to-time. The pin drive of the '370 machine requires precise control of its elevation because the carrier 23 meshes with the drive ring 31 supported by the ball bearing and not with the outer surface of the bolt itself.
U.S. Pat. No. 4,315,383 also shows the inner gear drive for an abrading machine. In particular, the '383 machine employs protective sleeves 47 and 48 which fit upon drive pins 44 and gear pins 21. The protective sleeves 47 and 48 are of a length greater than their corresponding pins and as such project above the top of the corresponding pins. The protective sleeves 47 and 48 also project into the enlarged counterbores 46 surrounding the openings which contain the gear pins so that the sleeves lie beneath the plane surface of the gear 32 and lap 16. This arrangement of protective sleeves, however, is not secured to the pins and as such may slip off during lapping and polishing. In addition, the use of enlarged counterbores without sealing rings allows for the potential intrusion of abrasives and deleterious substances within the openings 45 and the enlarged counterbores 46 which could eventually wear down the pins and cause the protective sleeves to loosen and slip off the pins.
It is therefore an object of my invention to take advantage of the fact that pins in a pin gear only rotate at a very small angle. By using a torsionally stretchable seal, the pin drags and stretches the seal during its slight rotation, yet always maintains a full contact with the seal. The seal guaranties a life time protection to the bearings from abrasive contamination during lapping and polishing operation.
It is a further object of my invention to also incorporate inner rings of miniature ball bearings into the pins so that the pin size can be maximized to provide maximum bolt rigidity.
It is a further object of my invention to provide a greater area of contact between the work carrier and the pin in order to minimize the elevational adjustment required.
It is another object of my invention to decrease the wear on the pins of lapping and polishing machines and to reduce the manufacturing costs of the process thereby, as well as to minimize the downtime of the machine.
A further object is to provide a second embodiment of my invention whereby a protective cap having a securing mechanism and optimal length is placed over each pin and rests upon the torsionally stretchable seal in order to increase the life of the pin, decrease its wear, and prevent the intrusion of slurries of abrasive materials from wearing down the pin and bonding the pin and seal. The protective cap can be readily replaced to minimize the downtime of the lapping and polishing machine. As will be described in greater detail hereinafter, the apparatus relating to the present invention differs from those previously proposed.
Other objects of my invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or apparent from, the following description and the accompanying drawing figures.